Polymer concentrates with improved processability

ABSTRACT

New polymer concentrates on the basis of polymer additives, like e.g. fillers and flame-retardants, are provided which have in particular an increased bulk density compared to the polymer additives as such. This increased bulk density leads to a substantial improvement in the processability of such concentrates, their dispersibility during compounding and the properties of the resulting polymer compound. Processing improvements include less dust, faster processing and more homogeneous additive dispersion. The invention also provides a process for preparing such new polymer concentrates, a process for preparing polymer compounds containing the new polymer concentrates, the respective polymer compounds and a process for preparing formed parts thereof. Such formed parts have more uniform properties such as density, wall thickness, and in case of the flame-retardants more homogeneous and consistent flame retardancy.

This application claims the benefit of European Application No.05025846.6 filed Nov. 26, 2005. This application is a Divisional of U.S.patent application Ser. No. 11/602,779 filed Nov. 21, 2006, currentlypending, entitled “New Polymer Concentrates with ImprovedProcessability”, the contents of which are hereby incorporated byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates to new polymer concentrates containing (1)one or more polymer additive(s) and (2) one or more polymer(s) whichcomprise repeating units of ethylene, vinyl acetate and optionally oneor more other monomers. The invention also relates to a process forpreparing such new polymer concentrates, a process for preparing polymercompounds comprising the new polymer concentrates, the resulting polymercompounds, a process for preparing formed parts thereof and the formedparts.

BACKGROUND OF THE INVENTION

Mineral hydroxides are an important class of polymer fillers used inparticular as flame retardants. Aluminium trihydroxide and magnesiumdihydroxide are the major examples of this class of fillers. However,these hydroxides as well as other finely powdered polymer fillers oradditives present problems in handling and particularly in compoundinginto polymers. Ideally, a finer particle size of solid polymer additivesshould lead to better dispersion in the polymer matrix, and betterdispersion equates to more efficient, uniform performance and improvedpolymer physical properties. Therefore, the solid polymer additivesoften have particle sizes reduced to less than 10 μm. On the other hand,finer particles are often more difficult to disperse and problems ofreagglomeration occur.

Additionally the general handling of finely powdered polymer additivespresents particular problems. One substantial problem of finely powderedpolymer additives is dusting. The creation of dust involves loss of rawmaterial, increased clean-up costs, and health concerns for thosehandling the solids.

Another problem is bulk density. Finer solids tend to have decreasedbulk density and increased packaging size, volume and cost. The fluffynature and low bulk density of finely powdered polymer additive solidsadversely affects additive flow properties, making them more difficultto meter when using continuous compounding equipment, such as twin screwextruders, but also making general handling difficult. Morespecifically, poor solids mixing homogeneity results in poor performancein general, for example poor physical properties in the final product.Finer solids tend to lead to, for example, poor physical properties inthe final product.

One prior art approach to increasing the mixing homogeneity in theaddition of low bulk density solids to polymers involves adding aliquid, such as a plasticizer, to the powder, prior to mixing the powderwith the polymer.

Blending the additive powder into the polymer in the form of amasterbatch concentrate that can be diluted with more polymer to achievethe desired final concentration of powder additive is a further commonapproach. It decreases dusting during the ultimate polymer processingstep. However, it not only adds a costly additional step, but it alsodoes not deal with the problem of poor mixing of a low bulk densityadditive powder and a polymer in forming the masterbatch concentrate. Infact, the masterbatch sometimes has poorer homogeneity because a higherproportion of incompatible fine powder is added. This method also has adisadvantage for fillers which are used in substantially larger amounts,such as flame retardants, due to the large amount of polymer carrierthat is included in the final compound.

The approach described in U.S. Pat. No. 4,849,134 to solving theseproblems is cold compaction of the filler. The disadvantage of thismethod is that compaction (re-)agglomerates the fine particles of theadditive. Unless subsequent polymer processing conditions result incomplete breakup of the coarse compacted, i.e. agglomerated particlesand dispersion into the polymer, any advantage of the fine particles islost.

The aim of increasing the bulk density of fine polymer fillers and inparticular flame retardants, flame retardant synergists, blends thereof,and other powdered polymer additives has significant value. Theseadditives are included in an amount of about 1% by weight to about 60%by weight, often 10-40% by weight, into a finished polymeric article.

Certain advantages of a lower bulk density polymer additive uponprocessing of one polymer, PVC, are referred to in U.S. Pat. No.3,567,669. This patent discloses a high speed mixing process whichrequires a temperature of at least 170° F. Under these conditions, thePVC particles have a slightly sintered or glazed surface. Solidadditives are absorbed or adsorbed onto the polymer surface.

U.S. Pat. No. 3,663,674 discloses densification of poly-α-olefins. Suchpoly-α-olefins are prepared in a dense granular form suitable formoulding or extrusion by the application of sufficient mechanical energyto compress and collapse the porous polymer particles recovered from thepolymerisation reactor. Cited advantages of increased bulk density areimproved handling characteristics and the lack of a thermal historyprior to processing. No mention is made of the effect of the bulkdensity of powdered additives upon the processability or properties ofthe polymer. Nor is there any mention of the use of flame retardants orflame retardant synergists.

Based upon the teachings of the U.S. Pat. No. 3,567,669 and U.S. Pat.No. 3,663,674 it was therefore the object of the present invention toprovide new concentrates of polymer additives, in particular fillers andflame-retardants, and polymers which new concentrates possess anenhanced processability, show an improved dispersability of the additivethroughout the polymer and eventually result in improved properties ofthe formed parts prepared by processing polymer compounds containing thenew concentrates.

SUMMARY OF THE INVENTION

The present invention is directed to a concentrate containing

-   (1) one or more polymer additives and-   (2) one or more polymers which comprise repeating units of ethylene,    vinyl acetate and optionally one or more other monomers,    wherein    -   (a) the concentrate contains less than 10% by weight of one or        more polymers (2), based on the total weight of the polymer        additive(s) (1) and the polymer(s) (2), and    -   (b) the concentrate is obtainable by mixing the polymer        additive(s) (1) with a solution of the polymer(s) (2) in a        solvent and removing the solvent,    -   (c) the mean primary particle size (“d₅₀”) of the polymer        additive(s) (1) prior to the mixing with the solution of the        polymer(s) (2) is less than 10 μm and    -   (d) the concentrate has a bulk density which is at least 50%        greater than that of the polymer additive(s) (1) prior to the        mixing with the solution of the polymer(s) (2), wherein such        bulk density is measured in accordance with DIN ISO 697 from        January 1984.

The present invention is further directed to a process for preparing theconcentrates by mixing the polymer additives (1) with a solution of thepolymer(s) (2) and removing the solvent.

Eventually the present invention is directed to the use of the inventiveconcentrates for preparing polymer compounds, to a process for preparingpolymer compounds comprising the concentrates, a process for preparingformed parts on the basis of such polymer compounds and the formedparts.

BRIEF DESCRIPTION OF DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawings, in which:

FIG. 1: is a chart of the particle size distributions for Examples 2b to2f.

DETAILED DESCRIPTION OF THE INVENTION

The polymer additive(s) (1) used to prepare the inventive concentrateshave a finely powdered form. The mean primary particle size (alsoabbreviated as “d₅₀”) of the polymer additive(s) (1) prior to subjectingthe polymer additive(s) (1) to the preparation of the inventiveconcentrate is less than 10 μm, preferably less than 5 μm, particularlypreferred less than 2.5 μm.

The term “mean primary particle size” (“d₅₀”) means that at least 50% ofthe polymer additive particles have a particle size less than 10 μm,preferably less than 5 μm, and particularly preferred less than 2 μm,and most preferably 0.5-1.5 μm. This mean primary particle size istypically measured by laser diffraction e.g. by using a MalvernMastersizer S.

The polymer additives (1) which may be used to prepare the inventiveconcentrates may be e.g. fillers, flame-retardants, flame-retardantsynergists, pigments or other finely powdered polymer additives or anymixtures thereof. This includes mixtures of different types of polymeradditives (1) may be used, e.g. a mixture of a filler and aflame-retardant or a mixture of a filler, a flame-retardant, and aflame-retardant synergist. Such polymer additives (1) are known andcommercially available. Usually it is not necessary to further reducethe particle size of the polymer additives (1) available.

As flame-retardants aluminium trihydroxide (ATH), magnesium hydroxide,antimony trioxide, or mixtures thereof are e.g. suitable.

As flame-retardant synergists zinc borate, antimony trioxide, sodiumantimonate, or mixtures thereof are suitable to additionally enhance theefficiency of the flame-retardant itself.

Suitable fillers subjected to the preparation of the inventiveconcentrates include carbon black, graphite, metal powders, talc, clays,mica, wollastonite, silica, calcium carbonate, hydrated minerals,boron-containing compounds, zinc-containing compounds,antimony-containing compounds, and mixtures thereof.

As pigments which can also be used in the present invention for exampleiron oxides and titanium dioxide are mentioned.

The polymer(s) (2) used to prepare the inventive concentrates compriserepeating units of ethylene, vinyl acetate and optionally one or moreother monomers. Such polymers are commercially available and aretypically produced by radical initiated polymerisation of ethylene,vinyl acetate and optionally one or more other monomers. Some commercialmaterials may also contain minor amounts of a third monomer such asacrylic acid or esters thereof. Such polymers are described in detail inUllmann's Encyclopedia of Industrial Chemistry 5^(th). Ed. 1993, VCHVerlagsgesellschaft, Vol. 23, page 241 ff and the references citedtherein. In particular, these polymers can be prepared in solution, forexample in tert. butanol or methanol. Before isolation of the polymerthese processes yield a solution of polymer and unreacted monomer in therespective solvent. Such solutions may be also be used in order toprepare the inventive concentrates.

The polymers (2) used may contain 40 to 90% by weight, preferably 60 to80% by weight vinyl acetate and 10 to 60% by weight, preferably 20 to40% by weight ethylene. In said polymers a percentage of the vinylacetate and/or ethylene may be replaced by one or more further monomers,e.g. 10 to 50% by weight of one or more further monomers, wherein thesum of all monomers in the polymer(s) (2) still has to give 100% byweight

Further monomer(s) encompass, but are not limited to, alkyl esters ofunsaturated mono- or di-carboxylic acids. Fumaric or maleic acid mono-or di-ethyl esters are particularly suitable.

It is an important feature of the invention that the concentratecontains less than 10% by weight of one or more polymers (2), based onthe total weight of the polymer additive(s) (1) and the polymer(s) (2).Preferably the concentrate contains 2 to 10% by weight, particularlypreferred 3 to 8% by weight and most preferably 3 to 6% by weight of oneor more polymers (2), based on the total weight of the polymeradditive(s) (1) and the polymer(s) (2).

The second object of this invention is a method of preparing suchconcentrates containing

-   (1) one or more polymer additives and-   (2) one or more polymers which comprise repeating units of ethylene,    vinyl acetate and optionally one or more other monomers,    comprising    -   mixing the polymer additive(s) (1) with a solution of the        polymer(s) (2) in a solvent, wherein the polymer additive(s) (1)        have a mean primary particle size (“d₅₀”) of less than 10 μm        prior to the mixing with the solution of the polymer(s) (2), and    -   removing the solvent,        wherein the concentrate has a bulk density which is at least 50%        greater than that of the polymer additive(s) (1) prior to the        mixing with the solution of the polymer(s) (2).

The polymer(s) (2) are used in a solution to prepare the inventiveconcentrates. Solvents which are typically used to prepare the solutionof the polymer(s) (2) are organic solvents like e.g. methanol, tert.butanol, toluene or methyl acetate. Typically the solution of thepolymer(s) (2) contains 70-99%.b.w of the solvent and 1-30% by weight ofthe polymer(s), based on the total amount of solvent and polymer(s),preferably 80-98% by weight of the solvent and 2-20% by weight of thepolymer(s). Additionally the solution of the polymer(s) may contain from2-20% by weight, preferably 4-10% by weight of vinylacetate, based onthe total amount of solvent, polymer(s) and vinylacetate.

In the next step the solvent is removed. Typically other volatiles maybe also removed together with the solvent.

To prepare the concentrate of the polymer additive(s) (1), preferablythe fillers, flame-retardants, flame-retardant synergists, pigments,other finely powdered polymer additives or any mixtures thereof, and thesolution of the polymer(s) (2) different processes can be used,especially in order to get a better redispersibility, higher bulkdensity, less trapped air, less dusting properties and betterflowability compared with the typically fine powder of fillers known asstate of the art. The processes which are suitable differ in the amountof solvent in the solution of the polymer(s) (2) that is used and whichtherefore has to be removed in the second step from the solid granules,pellets or tablets. For each process and the properties of the resultinggranules, pellets or tablets the amount of polymer remaining as binderin the granules, pellets or tablets as well as the amount of solventinitially present as moisture for plastizising, dispersing andgranulating, each related to the total amount of solids employed,determine the economics of the process as well as the particular methodused and the properties of the final granules, pellets or tablets.

The first process alternative of mixing the solid powder particles ofthe polymer additive(s) (1) with the solution of the polymer(s) (2) isto disperse the solid powder particles of the polymer additive(s) (1) inthe polymer solution by preparing a suspension in a stirred vessel oreven with additional deagglomeration forces for the solid powderparticles. Processes to be used for dispersing the solid powderparticles of the polymer additive (1) can be different types of stirrers(e.g. propeller, horseshoe, helix, tooth wheel), high shear dispersingunits (e.g. rotor-stator-mixers batch or continuous, colloid mills,corrundum disk mills), continuous powder dispersing units (e.g. jetpumps, powder draw in with rotor stator systems) or high energy systemssuch as a jet disperser, ultrasonic systems, roller mills or stirredmedia mills.

With these dispersing units the total solids content (this shall mean bydefinition the sum of the polymer additive(s) (1) and the polymer(s)(2)), is 5-80% by weight, preferably 10-70% by weight and particularlypreferred 20-60%, based on the total weight of the solution of thepolymer(s) (2) and the polymer additives (1).

Subsequent to the dispersing step the granules, pellets or tablets haveto be formed either in an integrated shaping and drying step such asfluidized bed granulation, spray granulation, vacuum drying in a mixergranulator or in a drying step such as spray drying or vacuum dryingwith a subsequent granulating step such as roller compaction ortableting.

Using the second process alternative less amount of solvent is needed:High shear machines for moist powders, pastes or suspensions are used inthis case. Typical machines are extruders such as single screwextruders, parallel rotating or counter rotating, twin screw extrudersor planetary extruders and kneaders such as co-kneaders orsigma-kneaders as well as other batch or continuous kneaders. With thesemachines, under high shear conditions, the solid powder particles of thepolymer additives (2) can be dispersed in the solution of the polymer(s)(1) and subsequently the mixture can be shaped by an integratedgranulation or a further shaping step such as low pressure extrusionwith frontal, radial or dome extrusion, pelletizing or granulating fromthe moist state of product. Such dispersing units work with total solidcontents of 5-99% by weight, preferably 50-95% by weight andparticularly preferred 55-90% by weight based on the total weight of thesolution of the polymer(s) (2) and the polymer additives (1).

The third and very effective process alternative to obtain granules,which generally employs even less solvent, is growth agglomeration byroll agglomeration or high shear agglomeration or combinations thereof.These processes work by moving the powdered particles of the polymeradditive(s) (1) e.g. in a vessel, on a pelletizer plate or in a mixingchamber. The solution of the polymer(s) (2) is then added either at onceas a batch, in a flow, as a semibatch or continuously, by sprayingeither semibatchwise or continuously. Under more or less intensivemixing the powder particles agglomerate by means of fluid bridges and agrowth agglomeration results.

Depending on the particular process which is used for this thirdalternative a more or less narrow particle size distribution resultswhich can be classified if desired in an integrated or subsequentclassifying process. The granulation process itself needs relativelysmall amounts of the solution of the polymer(s) (2). This third processalternative can be carried out with a total solid content of 20-99% byweight, preferably 50-95% by weight and particularly preferred 60-90% byweight, based on the total weight of the solution of the polymer(s) (2)and the polymer additives (1).

A very small amount of solvent is possible, when using the affinity ofthe fine powder of the polymer additives (1) to agglomerate because ofits surface forces. The affinity can be intensified and the stability ofthe resulting granules improved by moistening the solid powder of thepolymer additives (1) with a very small amount of polymer solution atthe beginning. The subsequent granulating process either can be a growthagglomeration or a dry pressure agglomeration e.g. roller compacting ortableting.

For most applications of the inventive concentrates in the form ofgranules the granules are required to be essentially solvent free. Howthe solvent is removed depends on the form of the moist product afterdispersion and/or granulation. Due to the necessity to ensure that noexplosion can occur vacuum drying is often used but also convective heatand mass transfer by static or vibrating fluidized bed drying (fluidizedbed), spray drying, continuous-flow drying, flash drying or radiationdryers are possible. Depending on the acceptable residual solvent a postdrying process (e.g. after a gentle convective drying process to obtaingranules of a certain strength) may be necessary. The concentrate may bealso subjected to a classifying, if this is deemed helpful.

Also a spheronising step before or after drying may be helpful, e.g. inorder to improve the flow behaviour of the granules, pellets or tabletsor to improve the particle size distribution as well as to abrade therough edges remaining after the granules, pellets or tablets have beenformed and dried. Such a step also reduces the dusting of the resultingproduct.

The preparation of granules, pellets or tablets and theircharacterisation is described in an article by M. Müller,Aufbereitungstechnik, 44, (2003), Nr. 2, page 22 ff and in an article byNold, Löbe and Müller, Interceram, 53, (2004), Nr. 2, page 96 ff.

It is a decisive feature of the inventive concentrate, of course afterthe removal of the solvent, that it has a bulk density which is at least50% greater than the one which the polymer additive(s) (1) have prior tothe mixing with the solution of the polymer(s) (2). This means that thepresent invention allows the preparation of solid concentrates with ahigh bulk density. Preferably the bulk density of the inventiveconcentrate is at least 100% greater than the one which the polymeradditive(s) (1) have prior to the mixing with the solution of thepolymer(s) (2).

The bulk density is measured in accordance with DIN ISO 697 from January1984.

The invention is further directed to the use of the inventiveconcentrates for preparing polymer compounds and to a process ofpreparing such polymer compounds containing the concentrates.

Such process of preparing polymer compounds containing the inventiveconcentrates comprises mixing the inventive concentrates with one ormore polymers (3).

Such polymers (3) encompass, but not limited to, nitrile rubber (alsoabbreviated as “NBR”), hydrogenated nitrile rubber (also abbreviated as“HNBR”), polyamides, polycarbonate, polyvinylchloride (“PVC”), AEM andEVM. All such polymers (3) are well-known and either commerciallyavailable or may be prepared by a person skilled in the art based onknown synthesis or manufacturing processes.

As used throughout this specification, the term “nitrile rubber” or“NBR” is intended to have a broad meaning and is meant to encompass anelastomer having repeating units derived from at least one conjugateddiene, at least one alpha-beta-unsaturated nitrile, and optionallyfurther one or more copolymerizable monomers.

The conjugated diene may be any known conjugated diene, preferably aC₄-C₆ conjugated diene. Preferred conjugated dienes are butadiene,isoprene, piperylene, 2,3-dimethyl butadiene and mixtures thereof. Evenmore preferred C₄-C₆ conjugated dienes are butadiene, isoprene andmixtures thereof. The most preferred C₄-C₆ conjugated diene isbutadiene.

The alpha-beta-unsaturated nitrile may be any knownalpha-beta-unsaturated nitrile, preferably a C₃-C₅alpha-beta-unsaturated nitrile. Preferred C₃-C₅ alpha-beta-unsaturatednitriles are acrylonitrile, methacrylonitrile, ethacrylonitrile andmixtures thereof. The most preferred C₃-C₅ alpha-beta-unsaturatednitrile is acrylonitrile.

Preferably, the copolymer contains in the range of from 40 to 85% byweight of repeating units derived from one or more conjugated dienes, inthe range of from 15 to 60 weight percent of repeating units derivedfrom one or more alpha-beta-unsaturated nitriles. More preferably, thecopolymer contains in the range of from 55 to 75 weight percent ofrepeating units derived from one or more conjugated dienes, in the rangeof from 25 to 40 weight percent of repeating units derived from one ormore alpha-beta-unsaturated nitriles.

Optionally, the copolymer may further contain repeating units derivedfrom one or more copolymerizable monomers, such as unsaturatedcarboxylic acids, alkyl acrylates and/or styrene. Repeating unitsderived from one or more copolymerizable monomers will replace eitherthe nitrile or the diene portion of the nitrile rubber and it will beapparent to the skilled in the art that the above mentioned figures willhave to be adjusted to result in 100% by weight

The “hydrogenated nitrile rubber” or “HNBR” means that the residualdouble bonds (RDB) present in the starting nitrile polymer/NBR arehydrogenated to a certain extent, typically more than 50% of theresidual double bonds are hydrogenated, preferably more than 90%, morepreferably more than 95% and most preferably more than 99% of theresidual double bonds are hydrogenated.

The term “polyamide” shall encompass homo- or copolymers which containmonomer repeating unit, which are linked by amide groups (—C(═O)—NH—).Examples of such polyamides cover polycaprolactam (nylon 6),polylaurolactam (nylon 12), polyhexamethylenadipate (nylon 6.6),polyhexamethylenazelamide (nylon 6.9), Polyhexamethylensebacamide (nylon6.10), polyhexamethylenisophthalamide (nylon 6, IP),polyaminoundecansaure (nylon 11), Polytetramethylenadipamide (nylon 4.6)as well as copolymers of caprolactame, hexamethylendiamine and adipicacid (nylon 6.6) and aramides like e.g. polyparaphenylenterephthalamide.

The term “polycarbonate” shall encompass the group of thermoplasticmaterials which can be formally considered to be a polyester fromcarbonic acid and aliphatic or aromatic dihydroxyl moieties.Economically the most important example are the polycarbonate producedfrom bisphenol A (2,2-(4,4-dihydroxy-diphenyl)-propane) and phosgene,but for particular properties other dihydroxy-diaryl-alkanes as well asother dihydroxy aromatic or aliphatic moieties can be included duringthe manufacturing process.

“Polyvinylchloride” or “PVC” shall be assumed to mean those polymersprepared by either suspension, emulsion or bulk polymerisation processesand based formally on the monomeric unit CH₂—CHCl. Those polymerscommercially available can also contain comonomers such as vinylacetate, vinylidene chloride or acrylonitrile. Additionally, PVC is alsoavailable which has been chlorinated after polymerisation and thesepolymers too are included within the scope of the present invention.

“Polyacrylates” or “AEM” is used herein to mean the polymers produced byan emulsion (co)polymerisation of, but not limited to, one or more ofthe following monomers: ethyl acrylate, butyl acrylate, methoxyethylacrylate, ethoxyethyl acrylate, caprolacton acrylate, 2-chloroethylvinyl ether, vinyl chloroacetate, p-vinyl benzyl chloride, allylglycidyl ether, glycidyl methacrylate, acrylic acid and methacrylicacid.

Eventually the invention concerns the polymer compounds containing theinventive concentrates and one or more polymers (3), a process forpreparing such polymer compounds as well as the formed partsmanufactured from the polymer compounds.

The preparation of the polymer compounds is typically achieved bycompounding the concentrates of the present invention with one or morepolymers (3). This compounding can be done by using for example aninternal mixer, a mixing extruder, such as a twin screw extruder or abus co-kneader.

The polymer compounds containing the inventive concentrates can be usedfor preparing formed parts thereof. Such formed parts may be profilessuch as sealing profiles or such as window profiles, equipment housingssuch as for computers and household or industrial electrical equipment,and for functional articles such as hoses and belts.

Such formed parts can be formed by extrusion, injection moulding orcompression moulding techniques and may be vulcanised (crosslinked)after forming to improve the mechanical properties of the finishedarticles.

The concentrates obtained by the process of this invention can bedescribed as low dusting during processing and are easy to meter andhandle. They maintain the fine particle size, and nevertheless show lowdusting. When being used for preparing polymer compounds, they aredispersed in the polymer faster and more efficient than the untreatedpolymer additive(s) and yield polymer compounds having improvedperformance due to the more uniform and homogeneous incorporation of thepolymer additive(s). Such increase of the compounding speed enhances thecommercial attractiveness of the processing.

Formed parts containing the inventive concentrates are more uniform withrespect to density, wall thickness, and more homogeneous compared toformed parts known so far. Physical properties such as flammability testperformance and/or impact strength also are enhanced.

Those skilled in the art would not have expected that increasing thebulk density of the specific polymer additives (1) by transferring theminto the inventive concentrates would enhance the processability,achieve better dispersion of the additive throughout the polymer, orenhance the properties of the processed polymer compound.

EXAMPLES

The concentrates of the present invention can be characterised visuallyto determine their tendency to form dust. A quantitative indication ofthe tendency to form dust can be derived from a sieve analysis.

The bulk density can be measured according to DIN ISO 697 from January1984.

The quality of the dispersion of the polymer additives (1), inparticular of fillers, in polymers and, in particular, in rubber can bemeasured by the shear modulus at varying amplitudes as described in A.R. Payne, R. E. Whittacker, Rubber Chem. Technol. 44, 440 (1971).

In the Examples Mg(OH)₂ was used as polymer additive (1), which has thetrade name Magnifin® H10A (Fa. Martinswerk, Germany) and a mean primaryparticle size (d₅₀) of 0.65-0.95 μm measured by laser diffraction usinga MALVERN MASTERSIZER S.

Examples 1a-d Preparing an Inventive Concentrate in the Form of FineGranules by Dispersing as a Polymer Additive (1) a Flame Retardant in anOrganic Polymer-Solution and Vacuum Drying of the Granules Example 1a

In a first example 1a 95 g of the flame retardant Mg(OH)₂, (Magnifin®H10A, Fa. Martinswerk) was dispersed in 155 g of a solution containing95 vol.-% of tert. butanol, 5 vol.-% vinyl acetate and 5 g of anethylene vinyl acetate copolymer itself containing 70% by weight vinylacetate and 30% by weight ethylene (Levapren®700, Lanxess DeutschlandGmbH, Germany). The flame retardant was dispersed by a batch labdisperser (Ultraturrax T18, Fa. IKA, Germany) for 5 minutes resulting inan increase of temperature of 10° C. The resulting suspension had asolid content of 40% by weight. After dispersion, the suspension wasdried at 20° C. in a lab extractor hood to yield a thick, solventcontaining, paste which was then vacuum dried at 40° C. for 48 h. Theresulting fine granules of Mg(OH)₂ contained 5% by weight ethylene vinylacetate copolymer.

This procedure was repeated for the following examples all employingMg(OH)₂ as a filler (Magnifin® H1M, Fa. Martinswerk) and the copolymerused in Example 1a.:

Example 1b

90 g of filler, 160 g of a solvent mixture (95 vol. % of tert. butanoland 5 vol. % of vinyl acetate), 10 g of ethylene vinyl acetatecopolymer.

Example 1c

98 g of filler, 152 g of a solvent mixture (95 vol. % of tert. Butanoland 5 vol. % of vinyl acetate), 2 g of ethylene vinyl acetate copolymer

Example 1d

99 g of filler, 151 g of a solvent mixture (95 vol. % of tert. Butanoland 5 vol. % of vinyl acetate), 1 g of ethylene vinyl acetate copolymer

Examples 2a-f

Preparing an inventive concentrate in the form of coarser granules byagglomerating as a polymer additive a flame retardant with an organicbinder solution containing an ethylene vinyl acetate copolymer andvacuum drying of granules.

In a second example coarse granules were produced by growthagglomeration in an intensive mixer (Eirich-Mixer R02, Fa. Eirich,Hardheim, Germany).

Example 2a

1000 g of flame retardant Mg(OH)₂ (Magnifin® H10A, Fa. Martinswerk,Germany) was placed in an “Eirich-Mixer”. The mixing was carried outunder a blanket of nitrogen (Level 1 of mixer vessel, 1500 U/min of apin mixing tool). 350 g of polymer solution containing 85.5% by weightof tert. butanol, 4.5% by weight vinyl acetate and 10% by weight of anethylene vinyl acetate copolymer, itself containing 70% by weight vinylacetate and 30% by weight ethylene (Levapren®700, Lanxess DeutschlandGmbH) was added in 3:30 min by a flexible tube pump to the dry powder.While the solution was added the granules grew and after a further 5 minof post mixing the granules were modified to a more narrow particle sizedistribution.

The granules were then dried at 20° C. in a lab extractor hood for 24 hand finally vacuum dried for 48 h at 40° C.

The resulting coarse granules contained 3.6% by weight ethylene vinylacetate copolymer.

This procedure was repeated for the following examples all employing asa filler Mg(OH)₂ (Magnifin® H1M, Fa. Martinswerk) and the copolymer usedin Example 2a:

Example 2b

1000 g of filler, 350 g polymer solution with 89.6% by weight tert.butanol, 4.7% by weight vinyl acetate and 5.7% by weight ethylene vinylacetate copolymer; mixing conditions: mixer vessel level 1, mixing tool750 U/min

Example 2c

1000 g of filler, 350 g polymer solution with 81.4% by weight tert.Butanol, 4.3% by weight vinyl acetate and 14.3% by weight ethylene vinylacetate copolymer; mixing conditions: mixer vessel level 1, mixing tool750 U/min

Example 2d

1000 g of filler, 350 g polymer solution with 85.5% by weight tert.Butanol, 4.5% by weight vinyl acetate and 10% by weight ethylene vinylacetate copolymer; mixing conditions: mixer vessel level 1, mixing tool750 U/min

Example 2e

1000 g of filler, 350 g polymer solution with 85.5% by weight tert.Butanol, 4.5% b.w vinyl acetate and 10% by weight ethylene vinyl acetatecopolymer; mixing conditions: mixer vessel level 1, mixing tool 1500U/min

Example 2f

1000 g of filler, 350 g polymer solution with 85.5% by weight tert.Butanol, 4.5% by weight vinyl acetate and 10% by weight ethylene vinylacetate copolymer; mixing conditions: mixer vessel level 1, mixing tool3000 U/min

The products from Examples 2b-2e were analysed by sieve analysis(vibrating lab sieve, 100 g, 30% intensity, 10 min) to determine theirparticle size distribution, but also to determine their fines contentwhich is an objective measure of their dusting characteristic.

All products had <1 wt.-% fines after drying; they did not dust whenshaken.

The particle size distributions are shown in the following Table 1 andin FIG. 1.

TABLE 1 Example 2b 2c 2d 2e 2f Sieved Fraction/% >4 mm 22.2 5.. 7.9 16.20 2-4 mm 60.8 40.6 49.3 40.4 21.2 1-2 mm 16.1 43.5 36.3 34.1 62.5 0.5-1mm 0.7 10.2 6.4 8.7 15.3 <0.5 mm 0.1 0.4 0.1 0.6 1.1

TABLE 2 Measurement of the bulk density of the granules of Examples 1and 2 in accordance with DIN ISO 697 from January 1984. EVA bulk densityTrial Parameters Sieve fraction* [% b.w.] [g/l] Comparative No mixing,analysed as As received 0 300 Example received (Magnifin ® H10A) Example2b Eirich-Mixer, 750 rpm no Classification after 2 825 GranulationExample 2c Eirich-Mixer, 750 rpm no Classification after 4.8 865Granulation Example 2d Eirich-Mixer, 750 rpm no Classification after 3.4855 Granulation Example 2e Eirich-Mixer, 1500 rpm no Classificationafter 3.4 845 Granulation Example 2f Eirich-Mixer, 3000 rpm noClassification after 3.4 800 Granulation Example 2b Eirich-Mixer, 750rpm Classifying fraction 2-4 mm 2 685 Example 2c Eirich-Mixer, 750 rpmClassifying fraction 2-4 mm 4.8 740 Example 2d Eirich-Mixer, 750 rpmClassifying fraction 2-4 mm 3.4 725 Example 2e Eirich-Mixer, 1500 rpmClassifying fraction 2-4 mm 3.4 745 Example 2f Eirich-Mixer, 3000 rpmClassifying fraction 2-4 mm 3.4 670 Example 1a Ultra-Turrax T18, noClassification after 5 485 20.000 rpm Granulation Example 1cUltra-Turrax T18, no Classification after 2 480 20.000 rpm Granulation*Column “Sieve Fraction” The entry “no Classification after Granulation”under “Sieve Fraction” means that the product as obtained aftergranulation was directly subjected to the measurement of the bulkdensity. The entry “Classifying fraction 2-4 mm” under “Sieve Fraction”means that the product obtained after granulation was subjected to aclassifying at first and the fraction obtained therefrom which had aparticle size of 2-4 mm was then subjected to the measurement of thebulk density.

Example 4 Processing the Granules from Examples 1 and 2 in a Polymer ona Two Roll Mill

The concentrates from Examples 1 and 2, as well as untreated Mg(OH)₂(comparative example) were mixed with an ethylene vinyl acetatecopolymer to produce a visually homogeneous sheet on a laboratory tworoll mill. The time taken to produce the apparently homogeneous sheetwas recorded.

The two roll mill (LaboWalz W80T; Vogt Maschinenbau GmbH) used had thefollowing specifications:

Roll diameter: 80 mm, Roll breadth: 280 mm, Roll speed: front: 16.5 Upm,back: 20 Upm, Friction: 1:1.2, Set temperature: 20° C.

For each experiment 50 g ethylene vinyl actetate copolymer (Levapren®700, Lanxess Deutschland GmbH, Germany) was put on the mill and acontinuous sheet formed. Thereafter, either the untreated filler(Mg(OH)₂) or the inventive concentrate was added as rapidly as possible.For the untreated filler the distance between the rolls (the nip) had tobe reduced to 0.5 mm in order to maintain the majority of the powder inthe bank of rubber in the nip. For all other experiments the nip wasmaintained at 0.7 mm.

The sheets from these experiments were used to measure the shear modulusat varying amplitudes and at a constant frequency of 10 Hz, atemperature of 60° C. using a Rubber Process Analyser (RPA 2000) made byAlpha Technology. The limiting shear modulus at zero amplitude can beseen as a measure of the quality of the dispersion of fillers in arubber matrix. The results as given in Table 2 below clearly show thatthe limiting shear modulus at zero amplitude is substantially lower andtherefore the dispersion of the filler in the matrix considered better,if the additive is not used untreated but in the form of the inventiveconcentrates.

TABLE 3 Time to visual Limiting Shear incorporation Modulus/kPaUntreated Filler* 490 s 900 Example 1a 240 s 730 Example 1c 260 s 740Example 2d 360 s 700 Example 2c 315 s 700 Example 2b 375 s 780 Example2e 405 s 725 Example 2f 470 s 750 Levapren 700** .-. 195 *Forcomparison: Mg(OH)₂ as Magnifin ® H10A, Fa. Martinswerk **Forcomparison, Levapren ® 700 (Lanxess Deutschland GmbH, Germany) wassolely used.

1. A concentrate containing (1) one or more polymer additives and (2) one or more polymers which comprise repeating units of ethylene, vinyl acetate and optionally one or more other monomers, wherein (a) the concentrate contains less than 10% by weight of one or more polymers (2), based on the total weight of the polymer additive(s) (1) and the polymer(s) (2), (b) the concentrate is obtainable by mixing the polymer additive(s) (1) with a solution of the polymer(s) (2) in a solvent and removing the solvent, (c) the mean primary particle size (“d₅₀”) of the polymer additive(s) (1) prior to the mixing with the solution of the polymer(s) (2) is less than 10 μm, and (d) the concentrate has a bulk density which is at least 50% greater than that of the polymer additive(s) (1) prior to the mixing with the solution of the polymer(s) (2), wherein such bulk density is measured in accordance with DIN ISO 697 from January
 1984. 2. The concentrate according to claim 1, wherein the mean primary particle size (“d₅₀”) of the polymer additive(s) (1) prior to the mixing with the solution of the polymer(s) (2) is less than 5 μm.
 3. The concentrate according to claim 1, wherein the mean primary particle size (“d₅₀”) of the polymer additive(s) (1) prior to the mixing with the solution of the polymer(s) (2) is less than 2 μm.
 4. The concentrate according to claim 1, wherein the mean primary particle size (“d₅₀”) of the polymer additive(s) (1) prior to the mixing with the solution of the polymer(s) (2) is in the range of from 0.5-1.5 μm.
 5. The concentrate according to claim 1, wherein the polymer additives (1) are fillers, flame-retardants, flame-retardant synergists, pigments, other finely powdered polymer additives or any mixtures thereof.
 6. The concentrate according to claim 5, wherein a mixture of a filler and a flame-retardant or a mixture of a filler, a flame-retardant, and a flame-retardant synergist is used.
 7. The concentrate according to claim 5 or 6, wherein as flame-retardants aluminium trihydroxide (ATH), magnesium hydroxide, antimony trioxide, or mixtures thereof are used.
 8. The concentrate according to claim 5 or 6, wherein as flame-retardant synergists zinc borate, antimony trioxide, sodium antimonate, or mixtures thereof are used.
 9. The concentrate according to claim 5 or 6, wherein as fillers carbon black, graphite, metal powders, talc, clays, mica, wollastonite, silica, calcium carbonate, hydrated minerals, boron-containing compounds, zinc-containing compounds, antimony-containing compounds, or mixtures thereof are used.
 10. The concentrate according to claim 5, wherein as pigments iron oxides or titanium dioxide are used.
 11. The concentrate according to claim 1, wherein the polymer(s) (2) contain 40 to 90% by weight vinyl acetate and 10 to 60% by weight ethylene and optionally 10 to 50% by weight of one or more further monomers, wherein the sum of all monomers in the polymer(s) (2) still has to give 100% by weight.
 12. The concentrate according to claim 1, wherein the polymer(s) (2) contain 60 to 80% by weight vinyl acetate and 20 to 40% by weight ethylene and optionally 10 to 50% by weight of one or more further monomers, wherein the sum of all monomers in the polymer(s) (2) still has to give 100% by weight.
 13. The concentrate according to claim 1, wherein the concentrate contains 2 to 10% by weight of one or more polymers (2), based on the total weight of the polymer additive(s) (1) and the polymer(s) (2).
 14. The concentrate according to claim 1, wherein the concentrate contains 3 to 8% by weight of one or more polymers (2), based on the total weight of the polymer additive(s) (1) and the polymer(s) (2).
 15. The concentrate according to claim 1, wherein the concentrate contains 3 to 6% by weight of one or more polymers (2), based on the total weight of the polymer additive(s) (1) and the polymer(s) (2).
 16. A method for preparing polymer compounds comprising mixing a concentrate according to claim 1 with one or more polymers (3).
 17. The method according to claim 16, wherein as polymers (3) nitrile rubber (“NBR”), hydrogenated nitrile rubber (“HNBR”), polyamides, polycarbonate, polyvinylchloride (“PVC”), AEM or EVM are used.
 18. A polymer compound comprising the concentrate according to claim 1 and one or more polymer(s) (3).
 19. The polymer compound according to claim 18 comprising as polymers (3) nitrile rubber (“NBR”), hydrogenated nitrile rubber (“HNBR”), polyamides, polycarbonate, polyvinylchloride (“PVC”), AEM or EVM.
 20. A process for preparing formed parts containing a polymer compound comprising processing the concentrate according to claim 1 with one or more polymer(s) (3).
 21. Formed parts of the polymer compounds according to claim
 19. 22. Formed parts according to claim 21 which are profiles, equipment housings, or functional articles.
 23. Formed parts according to claim 22 which are sealing profiles or window profiles, equipment housings for computers, household or industrial electrical equipment, hoses or belts. 